NZ236398A

NZ236398A - Production of shaped hydrogel articles

Info

Publication number: NZ236398A
Application number: NZ236398A
Authority: NZ
Inventors: Ture Kindt-Larsen; John C Heaton; Edmund C Rastrelli; Gregory A Hill
Original assignee: Vistakon Inc
Priority date: 1989-12-15
Filing date: 1990-12-07
Publication date: 1992-04-28
Also published as: HU908277D0; AU6808890A; ES2104591T3; KR100232615B1; DE69030915T2; AU626744B2; JPH04110311A; HUT56510A; PT96209A; IE79671B1; JP2941959B2; CA2032200A1; ZA9010079B; HK1000673A1; GR900100854A; NO905409D0; EP0433085A3; DK0433085T3; YU235390A; FI906179A0

Abstract

Shaped hydrogel articles such as soft contact lenses are prepared by (1) molding or casting a polymerization mixture comprising: (a) a monomer mixture comprising a major proportion of a hydrophilic (meth)acrylate ester such as 2-hydroxyethyl methacrylate, an alkyl (meth)acrylate wherein the alkyl group contains at least four carbon atoms, and a cross-linking monomer; and (b) a water-displaceable diluent, wherein said diluent has a viscosity of at least 100 MPa Sec at 30 DEG C, and wherein said diluent consists essentially of a boric acid ester of certain dihydric alcohols, said dihydric alcohols having Hansen polar (wp) and Hansen hydrogen bonding (wh) cohesion parameters falling within the area of a circle defined as having a center at wh = 20.5, wp = 13, and a radius of 8.5, to produce a shaped gel of a copolymer of said monomers and said diluent, and (2) thereafter replacing said diluent with water.

Description

<div class="application article clearfix" id="description"> 236398 .—v ' ',""«<»cW»»«on =°fn O V '-^to »J.5/OoV C.c3-t-- ' -JJ- ..A*-*®8' P.O. f.:p " •n.j.O-Ur- ■? o'i\ C'%»f _ o Patents Form No. 5 Number PATENTS ACT 1953 Dated COMPLETE SPECIFICATION METHOD OF FORMING SHAPED HYDROGEL ARTICLES INCLUDING CONTACT LENSES We, VISTAKON, INC of 1325 San Marco Boulevard, Jacksonville, Florida 32247, United States of America, a corporation organised under the laws of the State of Florida, United States of America do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - 1 - (followed by page la) 736398 5 10 15 20 30 35 VTN-26 The invention relates to the production of shaped hydrogel articles including soft contact lenses, and more particularly to a method for the direct molding of such articles using certain boric acid esters as water-displaceable diluents. Background of the Invention Until recently, soft contact lenses of the hydrogel type have been manufactured either by lathe cutting or spin casting. In the lathe cutting method, a lens blank or button of a substantially anhydrous hydrophilic polymer (xerogel) is mechanically cut and polished to a lens shape on a fine lathe, and thereafter is contacted with water or saline to hydrate the polymer and form the desired hydrogel lens. The mechanical steps utilized in the lathe cutting operation are similar to those used in the manufacture of hard contact lenses, except that allowance must be made for swelling of the lens during hydration of the polymer. In the spin casting method, a small quantity of hydrophilic monomer mixture is placed in a concave, optically polished mold, and the mold is rotated while the monomers are polymerized to form a xerogel lens. The two optical surfaces of the lens are formed simultaneously during polymerization, the outer surface being formed by the concave mold surface and the inner surface being shaped by the joint actions of centrifugal force generated f 5 10 15 20 25 30 35 6 236 39 8 - 2 - by the rotating mold and surface tension of the polymerization mixture. The lens produced thereby is contacted with water or saline to hydrate the polymer and form a hydrogel lens as in the case of the lathe cut lens. More recently, an improved process for producing hydrogel contact lenses has been developed, which method is not only more economical than either the lathe cut method or the spin casting method, but it has the advantage of enabling a more precise control over the final shape of the hydrated lens. This new method comprises the direct molding of a monomer mixture wherein said mixture is dissolved in a non-aqueous, water-displaceable solvent, the mixture is placed in a mold having the shape of the final desired hydrogel (i. e., water-swollen) lens, and the monomer/solvent mixture is subjected to conditions whereby the monomer(s) polymerize, to thereby produce a polymer/solvent mixture in the shape of the final desired hydrogel lens. (The polymerization must be carried out in a non-aqueous medium because water inhibits the polymerization reaction.) After the polymerization is complete, the solvent is displaced with water to produce a hydrated lens whose final size and shape are quite similar to the size and shape of the original molded polymer/solvent article. Such direct molding of hydrogel contact lenses is disclosed in Larsen, U. S. Patent No. 4,495,313 and in Larsen et al., U. S. Patent No. 4,680,336. In the Larsen patent, the water-displaceable diluents used are boric acid esters of polyhydric alcohols wherein the polyhydric alcohols have three or more hydroxyl groups. Alternatively, the polyhydric alcohols used may be a mixture of a polyhydric alcohol having three or more hydroxyl groups and a dihydric alcohol. See, for instance, the disclosure at Col. 3, lines 60 et seq. and . i i 236 3 - 3 - Col. 4, lines 18-22. The clear teaching of the Larsen patent is that the polyhydric alcohol used to prepare the borate esters for 5 use in the direct molding process of hydrogel contact lenses must have three or more hydroxyl groups. While it is disclosed that dihydric alcohols can be used in admixture with tri- and higher polyols, the tri- and higher polyols are essential components. 10 .-"""S An important aspect of this invention is based on the discovery that esters of boric acid and certain dihydric alcohols (as more fully defined below) can be used as water-displaceable diluents in a direct molding process 15 for making shaped hydrogel articles such as soft contact lenses from polymer mixtures containing as the principal monomer one or more hydrophilic (meth)acrylates such as 2-hydroxyethyl methacrylate ("HEMA"). The invention provides processing advantages in the direct molding 20 process for producing shaped hydrogel articles, including enhanced demoldability (i. e., the ability to open the mold after the polymerization with less force), which results in economic advantages such as a saving of labor costs, and a significant increase in yield because of a 25 reduced proportion of surface defects in the molded articles that would cause rejection. It is believed that the enhanced demoldability and significant improvement in yield is related to the fact that the boric acid esters of diols that are employed in this invention have a lower 30 surface tension than the preferred esters of the Larsen 'S ^ patent, No. 4,495,313, which reduces the adhesion of the polymer/solvent mixture to the mold. An additional significant advantage that is imparted to 35 the direct molding process by the water-displaceable VTN-26 >4 . t ) \ 5 10 15 20 25 30 35 6 236 398 - 4 - esters provided by this invention is an enhanced ability to employ hydrophobic monomers (such as UV-absorbing monomers) in the polymerization mixture. When one tries to include hydrophobic monomers such as UV-absorbing monomers in a monomer/diluent mixture using as the diluent the preferred esters of the said Larsen patent, it is found that the hydrophobic monomers are often not soluble in the mixture. Increasing medical awareness of the adverse affects of ultraviolet CUV") radiation on the eyes has led to the introduction of spectacles, goggles, contact lenses, and intraocular lenses containing a means to absorb UV radiation. With respect to both contact lenses and intraocular lenses made from polymers (usually acrylic polymers), the preferred means for imparting UV absorbing capability is to make the lens from a copolymer that contains a copolymerized UV-absorbing monomer. Such monomers are disclosed, for example, in Beard et al., U. S. Patent No. 4,528,311 and Dunks et al., U. S. Patent No. 4,716,234. It would be desirable to impart UV-absorbing properties to contact lenses made by the direct molding process by including UV-absorbing monomers in the monomer/diluent mixture. This invention makes this desired end practical. Soft contact lenses made from hydroxyalkyl (meth)acrylate polymers such as HEMA-based polymers are finding increased acceptance. Such polymers are used in fabricating daily wear contact lenses as well as extended wear contact lenses. One factor that affects the suitability of a contact lens for wear over an extended period of time is the oxygen transmissibility of the lens, since the cornea obtains oxygen directly from the air rather than from oxygen-carrying blood. Oxygen transmission through the , i •; > 5 10 15 20 25 30 35 26 236 3 - 5 - lens is essential for an extended wear lens, and is desirable for a daily wear lens. As a general rule, the more oxygen that is transmitted through the lens the better. One of the factors that affects the oxygen transmissibility of a contact lens is the thickness of the lens. The oxygen transmissibility of a contact lens is inversely proportional to the thickness of the lens. The comfort to the wearer of a contact lens is also inversely proportional to the lens's thickness. For these two reasons, i. e., to maximize oxygen transmission and to optimize comfort, if optical considerations permit, it is desirable to make HEMA-based contact lenses as thin as possible. The HEMA-based contact lenses that are available today usually vary in thickness from about 0.03 to about 0.6 millimeter in the hydrogel (water-swollen) state. The degree to which such lenses can be made thin is limited by the strength of the lens. Attempts to make them stronger (which would enable them to be made thinner) by increasing the proportion of polyfunctional cross-linker in the polymer are generally unsuccessful because the polymers also become more brittle when the cross-linking monomer proportion is increased beyond a certain point. The major novelty of this invention resides in the incorporation in a copolymer of a hydroxyalkyl (meth)acrylate such as 2-hydroxyethyl methacrylate of one or more Cg or higher alkyl (meth)acrylate comonomers. It has been found that such copolymers exhibit increased strength under conditions of low stress (that is, under the conditions of normal use) without a concurrent increase in brittleness, so that articles such as hydrogel contact lenses made from such copolymers can be made thinner. . - * T 1 5 10 15 20 25 30 35 26 236 39 - 6 - The prior art has incorporated hydrophobic monomers in hydrophilic polymers intended for use in soft contact lenses. For instance, such polymers are disclosed in Singer et al., U.S. Patent No. 4,620,954 and in Izumitani et al., U.S. Patent No. 4,625,009. In these patents the hydrophilic monomer is N-vinyl pyrrolidone or N,N-dimethyl acrylamide. Holcombe, in U. S. Patent Nos. 3,926,892 and 3,965,063/ has disclosed that lauryl acrylate or methacrylate can be a comonomer in a HEMA copolymer that also contains isobutyl methacrylate and either cyclohexyl methacrylate or N-(l,l-dimethyl-3-oxobutyl) acrylamide. The polymerization technique disclosed by Holcombe is bulk polymerization. No actual operative example of the use of lauryl methacrylate in the copolymer system contemplated by Holcombe is disclosed by Holcombe. In addition to the Holcombe patents, the Singer et al. patent, and the Izumitani et al. patent, all of which were cited above, Japanese Patent Nos. 61166516 and 61205901 (assigned to Hoya Corporation, the assignee of the Izumitani et al. patent) disclose contact lenses made from copolymers of N,N-dimethyl acrylamide or N-vinyl pyrrolidone and hydrophobic monomers. Dunks et al., in U.S. Patent No. 4,716,234, disclose the incorporation of certain benzotriazole (meth)acrylate esters in various polymers as UV absorbers. Among the many polymers mentioned are HEMA polymers. Benzotriazole (meth)acrylate esters are hydrophobic in nature. Seiderman, in U.S. Patent No. 3,503,942, discloses hydrophilic plastic contact lenses made from a bulk polymerized copolymer of hydroxyalkyl acrylate or methacrylate and up to about 35 wt% of an alkyl acrylate or methacrylate, some of which can be a Cjj_2Qalkyl V v D / •; 236398 - 7 - acrylate or methacrylate. Brief Summary of the Invention 5 Shaped hydrogel articles such as soft contact lenses are prepared by the steps of: (1) molding or casting a polymerization mixture comprising: (a) a monomer mixture comprising a major proportion 10 of one or more hydrophilic (meth)acrylate monomers such as 2-hydroxyethyl methacrylate, an alkyl (meth)acrylate wherein the alkyl group contains at least four carbon atoms, and one or more cross-linking monomers; and 15 (b) a water-displaceable diluent, wherein said diluent has a viscosity of at least 100 mPa.s at 30°C, and wherein said diluent consists essentially of a boric acid ester of certain dihydric alcohols, said dihydric alcohols having 20 Hansen polar (wp) and Hansen hydrogen bonding (w^) cohesion parameters falling within the area of a circle defined as having a center at w. = 20.5, w =13, and a h p radius of 8.5, 25 to produce a shaped gel of a copolymer of said monomers and said diluent, and (2) thereafter replacing said diluent with water. In an important aspect of the invention, soft contact 30 lenses are prepared by the steps of: (1) molding or casting a polymerization mixture comprising: (a) a monomer mixture comprising a major proportion of a hydrophilic (meth)acrylate 35 monomer such as 2-hydroxyethyl methacrylate, 1 ; I 5 10 15 20 25 30 35 :6 736398 - 8 - one or more cross-linking monomers, and an alkyl (meth)acrylate monomer wherein the alkyl group contains at least four carbon atoms; and (b) a water-displaceable diluent, wherein said diluent has a viscosity of at least 100 mPa.s at 30°C, and wherein said diluent consists essentially of a boric acid ester of certain dihydric alcohols, said dihydric alcohols having Hansen polar (w ) and JL Hansen hydrogen bonding (wh) cohesion parameters falling within the area of a circle defined as having a center at w^ = 20.5, Wp = 13, and a radius of 8.5, to produce a shaped gel of a copolymer of said monomers and said diluent, and (2) thereafter replacing said diluent with water. The Prior Art The Larsen patent (No. 4,495,313) cited above is the most relevant prior art known to Applicants with respect to the use of borate esters as water displaceable diluents in the preparation of molded or cast hydrogel articles. The Seiderman patent (No. 3,503,942) cited above is the most relevant prior art known to Applicants with respect to the use of copolymers of hydroxyalkyl (meth)acrylate and alkyl (meth)acrylate in the preparation of contact lenses. The Larsen et al. patent, No. 4,680,336, discloses the use in a direct molding process for making hydrogel articles of certain diluents that are selected on the basis of their viscosity and their Hansen polar and hydrogen bonding cohesion parameters. ' s ^ IT? "I 2.36 - 9 - Other U. S. patents relating to the direct molding of hydrogel articles such as soft contact lenses include Larsen, U. S. Patent Nos. 4,565,348 and 4,640,489, Ohkada et al., No. 4,347,198, Shepard, No. 4,208,364, and Wichterle et al., Re. 27,401 (No. 3,220,960). Other patents that disclose the preparation of contact lenses from hydroxyalkyl (meth)acrylates and alkyl (meth)acrylates are Masuhara et al., U.S. Patent No. 3,988,274, Tarumi et al., U.S. Patent No. 4,143,017, and Kato et al., U.S. Patent No. 4,529,747. Brief Description of the Drawings Fig. 1 is a plot of the Hansen cohesion parameters, w^ and Wp, for several dihydric alcohols; Fig. 2 is a calibration graph used in the determination of the Young's modulus of soft contact lenses; and Fig. 3 is a side view, partially schematic, of the test fixture and assembly used to determine the force required to open the molds in which contact lenses comprising polymer/diluent mixtures were produced. Fig. 4 is a front view of the same fixture and assembly shown in Fig 3. Detailed Description of the Invention A major novelty of the invention resides in the addition of C4 and higher alkyl (meth)acrylates to hydroxyalkyl (meth)acrylate copolymers intended for use in soft contact lenses. [As used herein, the expression M(meth)acrylate" is intended to represent "methacrylate and/or acrylate".] Such C4 and higher (meth)acrylate esters include, for example: n-butyl acrylate and methacrylate, /AF 11 5 X\ •;/'> <o O tn -1 ; n > Co „« ' <' » f-\ 5 10 15 20 25 30 35 26 2363 - 10 - n-hexyl acrylate and methacrylate, 2-ethylhexyl methacrylate and other octyl acrylates and methacrylates, n-decyl acrylate and methacrylate, isodecyl acrylate and methacrylate, dodecyl acrylate and mechacrylate, stearyl methacrylate, and other alkyl acrylates and methacrylates that have alkyl groups containing four or more carbon atoms. Preferably, the alkyl group in the alkyl (meth)acrylate contains a linear chain that is at least six carbon atoms long and up to, e.g., twenty carbon atoms long. The monomer mixture used in the invention contains a hydroxyalkyl (meth)acrylate such as HEMA, 2-hydroxyethyl acrylate, glycerol mono-acrylate, glycerol mono-methacrylate, or the like, as the major component, one or more polyfunctional cross-linking monomers, and optionally small amounts of other monomers such as methacrylic acid, as well as the Cg or higher alkyl (meth)acrylate. Other hydrophilic monomers that can be employed in the monomer mixture include 2-hydroxypropyl methacrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, N-vinyl pyrrolidone, and the like. The polyfunctional cross-linking monomers that can be employed, either singly or in combination, include ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, polyethylene glycol dimethacrylate (wherein the polyethylene glycol has a molecular weight up to, e. g., about 400), and other polyacrylate and polymethacrylate esters that contain two or more (meth)acrylate groups. The polyfunctional cross-linking monomer is used in the usual amounts, e. g., from about 0.1 to about 1.25 parts by weight per 100 parts by weight of hydroxyalkyl (meth)acrylate. Other monomers that can . a r> 23 6 3 - 11 - be used include methacrylic acid, which is used to influence the amount of water that the hydrogel will absorb at equilibrium. Methacrylic acid is usually employed in amounts of from about 0.25 to about 7 parts, 5 by weight, per 100 parts of hydroxyalkyl (meth)acrylate, depending, in part, upon factors such as the proportion of Cg or higher alkyl (meth)acrylate in the copolymer. As a general rule, more methacrylic acid will be used as the proportion of the alkyl (meth)acrylate monomer is 10 increased. The Cg or higher alkyl (meth)acrylate is used in an amount sufficient to enhance the elastic strength of the hydrogel comprising the water-swollen copolymer. Such amount is usually from about 10 to about 50 parts, and preferably from about 10 to 30 parts, by 15 weight, per 100 parts by weight of hydroxyalkyl (meth)acrylate such as HEMA. The monomer mixture can also contain one or more ultraviolet absorbing monomers. Illustrative of such 20 UV-absorbing monomers are the benzotriazole (meth)acrylate esters, for instance, the 2-[2'-hydroxy-5'-acryloyloxy-alkylphenyl]-2H-benzotriazoles disclosed by Beard et al. in U. S. Patent No. 4,528,311, the 2-[2'-hydroxy-5'-acryloyloxy-alkoxyphenyl]-2H-."7\ 25 benzotriazoles disclosed by Dunks et al. in U. S. Patent No. 4,716,234, and the 2-(2 *-hydroxyphenyl)-5(6)-(acryloylalkoxy)benzotriazoles disclosed by Dunks et al. in U. S. patent application Serial No. 21,096, filed on March 3, 1987, and assigned to an affiliate of the 30 assignee of this application. Specific illustrative benzotriazole UV-absorbing (meth)acrylate esters that can be used in the invention include the following compounds: 2-(2'-hydroxy-5'-methacryloxyethylphenyl)-2H-benzotriazole; 35 VTN-26 * r r^, 236 39 8 - 12 - 2-(2' -hydroxy-5 ' -methacryloxyethylphenyl)-5-chloro-2H-benzotriazole; 2-(2'-hydroxy-5'-methacryloxypropylphenyl)-5-chloro-2H-5 benzotriazole; 2-(21-hydroxy-5'-methacryloxypropyl-3'-tert-butylphenyl) ■ 2H-benzotriazole; 10 2-(2'-hydroxy-5'-methacryloxypropyl-3 *-tert-butylphenyl)-5-chloro-2H-benzotriazole; 2-[2 *-hydroxy-5'-(2-methacryloyloxyethoxy)-3'-tert-butylphenyl]-5-methoxy-2H-benzotriazole; 15 2-[2'-hydroxy-5 *-(gamma-methacryloyloxypropoxy)-31 -tert-butylphenyl]-5-methoxy-2H-benzotriazole; and 2-(3'-i-buty1-2'-hydroxy-5'-methoxyphenyl)-5-(3'-methacryloyloxypropoxy)benzotriazole. 20 Other UV-absorbing monomers that can be included in the polymerization reaction mixture include benzophenone derivatives, and the like. 25 The benzotriazole UV-absorbing (meth)acrylate esters are used in the monomer mixture in an amount effective to absorb UV radiation in the finished lens product. Usually, the proportion of the UV-absorbing monomer will be within the range of from about 1 to about 10 parts by N 30 weight per 100 parts by weight of the major hydrophilic ' monomer(s) such as HEMA. A polymerization catalyst is included in the monomer mixture. The polymerization catalyst can be a free 35 radical generating compound such as lauroyl peroxide, VTN-26 236398 - 13 - benzoyl peroxide, isopropyl percarbonate, azobisisobutyronitrile, or the like, that generates free radicals at moderately elevated temperatures/ or the polymerization catalyst can be a photoinitiator system 5 such as a tertiary amine plus a diketone. One illustrative example of such a photoinitiator system is camphorquinone and ethyl 4-(N,N-dimethylamino)benzoate. Another illustrative photoinitiator is 4-(2-hydroxyethoxy)phenyl 2-hydroxy-2-propyl ketone. The 10 catalyst is used in the polymerization reaction mixture in catalytically effective amounts, e. g., from about 0.25 to about 1.5 parts by weight per 100 parts of hydroxyalkyl (meth)acrylate. 15 The boric acid esters are esters that are used in the invention as water-displaceable diluents in the direct molding of hydrogel articles comprise borate esters of certain dihydric alcohols, said dihydric alcohols having Hansen polar (wp) and Hansen hydrogen bonding (wh) 20 cohesion parameters falling within the area of a circle defined as having a center at = 20.5, wp = 13, and a radius of 8.5. It is also required that the ester of boric acid and the dihydroxy compound have a viscosity of at least 100 MPa Sec at 30°C, and preferably at least "2^ 25 about 500 mPa. s at 30°C. The boric acid esters are prepared by procedures analogous to those that are known in the art, as by reacting boric acid with the dihydric alcohol (for brevity, dihydric 30 alcohols will occasionally be referred to herein as "diols" ) and removing the water formed by the reaction by normal procedures such as by vacuum distillation. The reaction of boric acid with the dihydric alcohol is carried out at a temperature and for a period of time 35 sufficient to form the ester. Typical reaction VTN-2 6 236398 n n s"~*\ - 14 - temperatures are usually found within the range of from about 50° to about 120°C. At these temperatures, reaction times of from about two to about twelve hours are typical. In any event, the reaction is continued until 5 the water content of the ester is less than about 2%, by weight. The proportion of boric acid to dihydric alcohol is selected so that the viscosity of the ester is at least 100 mPa.s at 30°C. The examples, below, give representative proportions of boric acid to dihydric 10 alcohol that have been found to give the desired viscosity in the ester product. In certain cases, it may be desirable to include a small proportion of a monohydric alcohol in the esterification reaction mixture to control the molecular weight of the ester product. 15 The dihydric alcohols used in preparing the water-displaceable borate ester diluents used in the invention are those having Hansen polar (wp) and Hansen hydrogen bonding (w^) cohesion parameters 20 falling within the area of a circle defined as having a center at w^ = 20.5, wp = 13, and a radius of 8.5. The Hansen cohesion parameter w is usually expressed in terms of three components (w^, wp, w^) where w^ is the hydrogen bonding cohesion 25 parameter, wp is the polar cohesion parameter, and Wg is the dispersion cohesion parameter. It has been found that for the purposes of this invention the dispersion cohesion parameters of the dihydric alcohols are substantially the same (the values that have been 30 determined vary between about 15.7 and 17.0), and therefore have little effect in determining the suitability of any particular dihydric alcohol for use in the invention. The consideration of the Hansen cohesion parameters for the dihydric alcohol used in making the 35 borate ester diluent is accordingly reduced to a VTN-2 6 r-t i 5 10 15 20 25 30 35 6 236398 - 15 - two-dimensional function on the basis of polar and hydrogen bonding cohesion parameters. Hansen cohesion parameters are known in the art. Reference is made to "CRC Handbook of Solubility Parameters and Other Cohesion Parameters", by Allan F. M. Barton/ CRC Press# Inc., Boca Raton, Florida (1983), especially pages 85-87, 141, and 153-164, Hansen, "THE UNIVERSALITY OF THE SOLUBILITY PARAMETER", I&EC Product Research and Development, Vol. 8, No. 1, March 1969, pages 2-11, Wernick, "Stereographic Display of Three-Dimensional Solubility Parameter Correlations", Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 2, 1984, pages 240-245, and Kirk-Othmer Encyclopedia of Chemical Technology, 2nd ed., Suppl. Vol., Interscience, NY 1971, pages 891 and 892, for illustrative discussions of the Hansen cohesion parameters and how to determine them. The Hansen cohesion parameters, wh and wp, for selected polyhydric alcohols are displayed in Table I, below. The Hansen and Beerbower data as reported in the CRC Handbook were used when available. For diols that were not listed, the values were calculated from group contributions using the Hansen and Beerbower data as shown in the CRC Handbook, pp. 85-87 and Kirk-Othmer, pp. 891-892. The values for w„ were calculated by the P simple additive method as suggested in Kirk-Othmer. 236398 - 16 -Teble I HANSEN PARAMETERS OF DIHYDRIC ALCOHOLS DIOL ABBREVIATION w w. P n ETHYLENE GLYCOL EG 11.0 26.0 1,2-PROPANEDIOL 1,2-PD 9.4 23.3 1/3-PROPANEDIOL 1,3-PD 14.0 23.2 10 1,2-BUTANEDIOL 1,2-BD 7.7 20. 8 1,3-BUTANEDIOL 1,3-BD 10.0 21.5 1,4-BUTANEDIOL 1,4-BD 10.0 21.5 2/3—BUTANEDIOL 2,3-BD 7.7 20. 8 1,6-HEXANEDIOL 1,6-HD 8.4 17.8 15 2,5—HEXANEDIOL 2,5-HD 8.4 17.8 1/8—OCTANEDIOL 1,8-OD 6.3 15.5 1,lO-DECANEDIOL 1,10-DD 5.0 13.8 DIETHYLENE GLYCOL DEG 14.7 20.5 POLYETHYLENE GLYCOL (400 mw) PEG 400 11.6 14.5 20 POLYETHYLENE GLYCOL (1000 mw) PEG 1000 10.9 12. 6 DIPROPYLENE GLYCOL DPG 20.3 18.4 TRIPROPYLENE GLYCOL TPG 9.8 16.1 POLYPROPYLENE GLYCOL (4 00 mw) PPG 400 8.3 12.9 25 The data presented in Table I is displayed as a plot of w. versus w„ in Fig. 1. n P The examples set forth below illustrate the practice of the invention. In the examples, all parts are by weight, 30 unless otherwise indicated. VTN 35 -26 . ■>) 1 n 30 - 17 -EXAMPLE 1 23 6 398 Illustrative molding procedure. 5 Contact lenses are molded from the following polymerization reaction mixture: Component Parts, by Weight HEMA 100.0 10 Methacrylic acid 2.00 Ethylene glycol dimethacrylate 0.4 Darocure 1173^1^ 0.35 1,4-butanediol Boric Acid Ester^2^ 102.75 15 4-(2-hydroxyethoxy)phenyl 2-hydroxy-2-propyl ketone (2\ v ' Produced by reacting 797 parts, by weight, of 1,4-butanediol with 203 parts, by weight, of boric acid at a temperature of 90°C for 4 hours under 750 mm Hg vacuum. 20 The polymerization reaction mixture is placed in transparent polystyrene molds of the type described in Larsen, U. S. Patent No. 4,640,489 (see, especially, Fig. 2 of the Larsen patent), and is exposed on one side of the 2 25 polystyrene mold to 1.7 Joules/cm of ultraviolet radiation for 6 to 12 minutes (the exact exposure time is not narrowly critical). EXAMPLE 2 Illustrative monomer/diluent recipe for UV-absorbing lens. Using conditions analogous to those described above in Example 1, contact lenses are molded from the following 35 polymerization reaction mixture: VTN-26 . i ■: 236 398 - 18 - Component Parts, bv Weight HEMA 100.00 Methacrylic acid 2.04 Ethylene glycol dimethacrylate 0.4 5 2-(2'hydroxy-5'-methacryloxypropyl-3 *-i-butylphenyl)-5-chloro-.2H-benzotriazole 3.00 Camphorquinone 0.40 Ethyl 4-(N,N-dimethylamino)benzoate 0.60 10 1,4-butanediol Boric Acid Ester^1^ 77.45 Produced by reacting 797 parts, by weight, of 1,4-butanediol with 203 parts, by weight, of boric acid at a temperature of 90°C for 4 hours under a vacuum of 750 mm 15 Hg. EXAMPLE 3 20 A series of esters of boric acid and dihydric alcohols were made by the following general procedure: The boric acid and dihydric alcohol were charged to a 1-liter rotating evaporator and gradually heated to 90°C 25 (the time to achieve 90°C was about 1 hour), while applying mild vacuum (100 torr). When 90°C was reached, a full vacuum (10 torr) was applied and the reaction was continued for 3 hours at 90°C. After cooling, water content was determined by Karl Fischer titration and the 30 viscosity of the borate ester at 30°C was determined by a Brookfield LVF viscometer (6, 12, and 30 rpm). The borate esters that were prepared in accordance with the foregoing general procedure are identified in Table 35 II, below. The table identifies the diols used, using the VTN-2 6 236 3 - 19 - abbreviations mentioned in Table I, and one triol, glycerol ("gly"), that was used as a control, the mols of each component (alcohol and boric acid) and the molar ratio of the alcohol to boric acid reactants used to prepare each ester, the viscosity at 30°C (in mPa Sec), and the per cent of water in the ester. A column for comments is also included in the table. - 20 -TABLE II 236398 tms For 10 00 Molar gms Of ratio, 5 Reactants ale Water Vise., Acid AlC to cont., mPa sec Run Alcohol Mo Is Mo Is acid % 30°C Comments 1 EG 3.75 12.38 3.30 0.5 Paste 10 2 EG 4.36 11.77 2.70 1.7 solid (1) 3 1,2-PD 3.91 9.97 2.55 0.3 85 4 1,2-PD 5.03 9 .05 1.80 0.7 200 5 1,2-PD 5.68 8. 52 1.50 1.4 632 (2) 6 1,3-PD 3.45 10.34 3.00 0.7 38 15 7 1,3-PD 5.68 8.52 1.50 1.4 40 8 1,2-BD 3.28 8.85 2.70 0.2 50 9 1,2-BD 5.08 7. 61 1.5 1.1 100 (2) 10 1,3-BD 5.08 7.61 1.50 1.0 100 11 1,4-BD 3.01 9 .03 3.00 1.8 1200 20 12 1,4-BD 3.28 8.85 2.70 1.4 14000 13 2,3-BD 3.28 8.85 2.70 0 48 14 2,3-BD 5.08 7.61 1.50 1.1 50 (2) 15 1,6-HD 2.63 7.09 2.70 0.3 27250 (3) 16 2,5-HD 2.40 7.21 3 . 00 0.4 15200 (3) 25 17 2,5-HD 2.63 7.09 2. 70 0.4 100000+ (2),(3) 18 1,8-OD 2.09 5.96 2.85 0.3 solid (1)/(3) 19 1,10-DD 1.88 5 .07 2.70 0.3 solid (4) 20 GLY 4.06 8.13 2. 00 0.6-1 18-22000 21 DEG 2.87 7.75 2.7 1.3 870 30 22 PEG 400 0.88 2.36 2.70 0.7 590 23 PEG 1000 0.362 0 .978 2.70 0.7 Solid (1) 24 DPG 2.36 6.37 2.70 1.3 2360 25 DPG 2.75 6 .19 2 . 25 1.5 100000+ 26 TPG 1.72 4 . 65 2. 70 0.9 1000 35 27 PPG 4 00 1.04 2.34 2.25 0.9 900 (4) VTN-26 - 21 - ?36398 o 10 ) 15 20 30 35 VTN-2 6 (1) Diluent solid, but useable when mixed with monomers. (2) Boric acid crystals formed when mixed with water. (3) Not completely compatible with water (in a mixture of 1 part ester to 10 parts water, by weight), but can be used because it is displaceable after a wash with ethanol or a mixture of ethanol and water. (4) Not compatible with either water or monomer mixture (1:1 monomer:diluent, by weight); cannot be used. Many of the borate esters identified above in Table II were evaluated as water-displaceable diluents with the following monomer formulation: Component Parts , bv Weight HEMA 100.0 Methacrylic acid 2.0 Ethylene glycol dimethacrylate 0.4 Darocure 1173 0.35 Diluent 102.75 This monomer formulation, which contains 0.4 part of cross-linking monomer, was selected for evaluation because the Young's modulus values of the hydrogels prepared from this formulation can be correlated well with expected performance in the contact lens application. It has been found that if the Young's modulus of a hydrogel prepared using this formulation (which includes 0.4 part of a polyfunctional cross-linking monomer) is at least about 0.10—0.12 mPa, then a hydrogel prepared from a similar formulation, which may contain a slightly higher proportion of cross-linking monomer, can be expected to be strong enough for use as a soft contact lens. In conventional commercial practice, the amount of rrt n 236398 O 10 15 20 'w* 25 30 35 VTN-26 polyfunctional cross-linking monomer(s) such as ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate is normally from about 0.2-1.0 part in a formulation similar to that used in this Example. Soft contact lenses were prepared from the monomer/diluent mixtures set forth above in transparent polystyrene molds as described above in Example 1. The monomer/diluent mixture in each mold was exposed on one side to about 1.7 Joules/cm of ultraviolet radiation for 10 minutes at 55°C (TL09 lamps, with peak radiation at 350 nm). The lenses prepared from the diluent/monomer mixtures were evaluated for: (1) Appearance of lens, both in the mold and after demolding; and (2) Young's modulus of the hydrated lens; and (3) Force required to demold the molded lenses. The results of these evaluations are displayed in Tables III and IV, below. Table III displays the Run No., the dihydric alcohol used to make the borate ester diluent, lens appearance (C=clear, W=white, OS=opaque surface, SO=slightly opaque), and the Young's modulus "E", in mPa. Table IV displays the force required to demold the molded lenses at three different temperatures. n n 236 398 - 23 -TABLE III EVALUATION OF MOLDED LENSES 5 Ester No Alcohol ADDearance Mold Final E Comments 1 EG C c .20 2 EG C c .23 3 1,2-PD C c .11 4 1,2-PD C c .18 10 5 1,2-PD C c/os .17 (1) 7 1,3-PD - c/os - (2) 8 1,2-BD c c .25 9 1,2-BD OS - - (2) 10 1,3-BD OS - - (2) 15 11 1,4-BD c c .24 13 2,3-BD c c .08 14 2,3-BD OS - - (2) 15 1,6-HD c c .19 16 2,5-HD c c .19 20 18 1,8-OD c so .21 20 GLY c c .25 (control) 21 DEG c c .29 22 PEG 400 c c .34 23 PEG 1000 c c .30 25 24 DPG c c .28 25 DPG c c .27 26 TPG c c .27 27 PPG 400 w w — 30 (1) Dissolved the polystyrene mold slightly which caused a slightly opaque surface. (2) Dissolved the polystyrene mold; could not be demolded, 35 VTN-26 V 'I "\ / 5 10 15 20 25 30 35 6 236398 - 24 - Modulus test. The Young's modulus values of the lenses displayed in Table III were determined by the following procedure: Scope This test is useful for comparative non-destructive modulus testing of lenses of almost identical physical dimensions. The test has been calibrated against similar lenses tested in an accurate test as described in Larsen et al., U. S. Patent No. 4,680/336 (column 9-10). Lenses The lenses useful in this test are a -1.0 diopter, 8.9 +/-0.3 mm BC (base curve), 0.15 +/- 0.01 mm center thickness, 14.0 +/- 0.5 mm diameter. Test The lens dimensions are measured and, if within the specification, the lens is placed on top of a transparent acrylic cylinder (13 mm outer diameter, 9.8 mm inner diameter, 7.2 mm height) so that the lens front curve rests against the inner (9.8 mm diameter) top surface of the acrylic cylinder. The set-up is immersed in 0.9% saline in the center thickness-measuring chamber of an Optimec JCF/R/SI Contact Lens Analyzer. The cylinder and lens are centered so that the lens is in a horizontal position, and the center thickness scale is adjusted so that it can measure deflection on the center of the front curve surface. A 3 mm stainless steel ball (weight 0.2584 gram) is 23 6 3! - 25 - carefully placed on the concave side of the lens. The central part of the lens will deflect depending on the modulus of the lens. The deflection is read in mm on the center thickness scale, and the modulus can be determined from the calibration graph, Fig. 2. 10 A minimum of 3 lenses from the same batch are being tested, and the deflection of each lens is measured 3 times. The modulus is the average of at least 9 measurements. 15 20 25 30 Ester Table IV Demold Force Demold Force (lbs) No. Diol 30° c 55°C 80 °c 1 EG 6 .49 1.11) 5 .15 4. 76 (1 .08) 2 EG (1 N/A (2) 6. 15 (0 .54) 3 1,2-PD 3 .94 0.43) 2 .87 (0.52) 2. 73 (0 .52) 4 1,2-PD 4 .53 0.32) 3 .20 (0.42) 3. 26 (0 .75) 5 1,2-PD 1 .46 0.77) 1 .99 (0.87) 2. 39 (1 .03) 6 1,3-PD 3 .95 0.38) 3 .11 (0.63) 2. 68 (0 .25) 7 1,3-PD (3 (3) (3) 10 1,3-BD (3 (3) (3) 11 1,4-BD 4 .99 0.63) 4 .51 (0.47) 3. 44 (0 .53) 12 1,4-BD 5 .70 0.33) 3 .91 (0.91) 3. 50 (0 .31) 20 GLY (1 (1) (1) 21 DEG 2 .81 0.66) 2 .42 (0.71) 1. 56 (0 .64) 22 PEG 400 3 .39 0.36) 2 .76 (0.51) 1. 36 (0 .43) 23 PEG 1000 3 .47 1.01) 3 .53 (0.57) 3. 03 (0 .71) 24 DPG 0 .86 0.49) 1 .08 (0.41) 1. 18 (0 .18) 25 DPG 0 .92 0.21) 0 .76 (0.32) 1. 11 (0 .52) 26 TPG 1 .75 0 .57) 1 .76 (0.61) 2. 18 (0 .35) 27 TPG (4) (4) (4) 35 VTN-2 6 - 26 - 0 The numbers in parentheses are standard deviations. (1) The flange on the top half of the mold broke during force measurement. (2) Data not available (3) Not possible to demold. The polymer/diluent mixture dissolved the mold and bonded the two halves of the mold together. (4) Demold force too low to measure. Demold test. The test employed to evaluate the force reguired to open the mold in which the polymer/diluent mixtures were produced, the results of which are displayed in Table IV, is as follows: This test is useful for quantifying the minimum force required to separate the front and back halves of the mold (as described in Larsen, U. S. Patent No. 4,640,489) which are bound together by a polymer matrix containing some known level of diluent. The mold dimensions should remain constant for all samples analyzed. Instrumentation The test fixture and assembly used to measure the forces to open the molds is shown in Figs 3 & 4. In Fig. 3 the instrument used for measuring the force is a laboratory testing apparatus 10, such as Instron model #1122. A 50 lb load cell (not shown) is used with the chart recorder 12 being set at 20 lbs full scale. Scope 36398 *1 10 - 27 - The temperature is controlled by a heat gun (not shown), such as a Varitemp heat gun (Model VT-750A) connected to a Staco type 3PN2210 rheostat. A T-type thermocouple (not shown) inserted in the polymer/diluent mixture is used to measure the temperature of the polymer/diluent mixture. Referring to Fig. 4, a fixture-14 holds the specimen 16 in place during the test and a lever 18 is used to pull the top half 20 of the mold away from the bottom half 22. Test Procedure The specimen is comprised of the top 20 and bottom 22 halves of the mold 16, which are bound together by the 15 polymer/diluent matrix 24. The specimens for testing are freshly produced filled molds of constant dimensions. The molds are placed in a dessicator immediately after polymerization so as to prevent moisture from being absorbed by the polymer or the diluent. 20 The specimen to be tested is placed in the sample holder as shown in Fig. 3. The sample fixture is held by the lower grip of the Instron with a pressure of 36 PSI. The entire specimen is situated at a 20° angle to the 25 horizontal plane when placed in the fixture. The bottom half 22 of the mold is kept in place during the test by inserting four pins (only two are shown, in cross-section) 26, 28 around the circumference of the bottom half 22 of the mold at 90° intervals. O 30 The lever 18 used to pull the top half 20 away from the bottom half 22 is positioned between the two halves and is held in place by the upper grip 30 of the Instron. The rate at which the lever pulls the top half is controlled 35 by the cross-head speed of the Instron. r" * 'I A VTN-26 ;> J® •' £ o !?/■ NO 28 The air flow of the heat gun is directed directly at the top half of the mold to maintain consistent heating. The temperature of the air flow can be controlled with the rheostat. The sample temperature is monitored by inserting a thermocouple in such a way as to measure the change in temperature of the polymer/diluent matrix 24. When the thermocouple measures the desired temperature, the cross-head of the Instron is raised at a speed of 1 inch/min. The force to demold was measured at 30°, 55°, and 80°C. The force required to break the adhesion of the polymer/diluent to the top half 20 as a function of time if recorded by the chart recorder of the Instron. From this recording, the minimum demold force is determined. From the data presented above, it can be seen that only those esters made from diols falling within the defined Hansen parameter area give transparent lenses (which is essential for the contact lens application), and only those having viscosities greater than 100 mPa.s have modulus values high enough to be strong enough to be used in the contact lens application. The demold data clearly demonstrate that the diol esters of this invention give much easier demoldability (less force needed to demold) than do the preferred esters of the Larsen patent, No. 4,495,313. As an illustration of the yield improvement that can be obtained by employing the diol-borate esters of this invention in place of a glycerol-borate ester, the number of surface flaws was determined on three batches of 80 . -i ■ n 236 398 - 29 - lenses from each of monomer/ester mixtures, using a formulation analogous to that set forth above in Example 1. When the diluent used was a diethylene glycol/boric acid ester (ester No. 21 in Table II), the percentage of 5 surface defects was found to be 10.4%, when the diluent was a 1,4-butanediol/boric acid ester (ester No. 12 in Table II), the percentage of surface defects was found to be 13.0%, and when the diluent was a glycerol/boric acid ester (ester No. 20 in Table II), the percentage of 10 surface defects was found to be 30.4%. This is a valuable improvement over the process taught in the Larsen patent, No. 4,495,313. 15 Example 4 Preparation of Alkyl (Meth)acrylate Modified HEMA Using Borate Ester Water-Displaceable Diluent. To the following: 20 102.llg hydroxyethyl methacrylate (HEMA) 3.82g methacrylic acid (MAA) 0.85g ethylene glycol dimethacrylate (EGDMA) 0.10g trimethylolpropane trimethacrylate (TMPTA) 0.36g DAROCURE^1* (2 ) 25 136.75g water-displaceable diluent , 4-(2-hydroxyethoxy)phenyl 2-hydroxy-2-propyl ketone. (2} v ' Produced by reacting 1094.84 parts, by weight, 1,4-butanediol with 278.64 parts, by weight, boric acid at 30 a temperature of 90°C for 2 hours under a pressure of 10 torr in a rotating evaporator. was added 20.Og of an alkyl (meth)acrylate or other 35 hydrophobic ester of methacrylic acid. The monomer VTN-2 6 236398 - 30 - mixture was placed in a vacuum oven at 40 mm Hg for 3 hours to remove the oxygen. The vacuum oven was then filled with nitrogen gas. Clear polystyrene contact lens molds of the type shown in Fig. 2 of Larsen, U. S. Patent 5 No. 4,640,489, were filled with the selected mixture in a nitrogen filled glove box. The filled frames were polymerized by exposure on one side to about 1.7 Joules/cm2 of UV light from Philips TL40W/09n fluorescent bulbs with a maximum output at 365 nm. The —10 exposure to UV light was carried out for about 10 minutes (the exact time is not narrowly critical) . After polymerization, the polymer/diluent mixture was washed with a 50:50 ethanol:water (by volume) mixture, followed by a wash with pure water to displace the diluent with 15 water. The lens was then packed in standard soft contact lens packing solution (buffered saline) for storage. Table V, below, displays the hydrophobic group of the methacrylic ester, the appearance of the hydrogel (i. e., 20 the polymer swollen with water), the percent of water in the hydrogel, the compression modulus (referred to as "stiffness") of the hydrogel, and the oxygen transmissibility of the hydrogel. w' 25 The stiffness of the hydrogel was measured by the following procedure: Compression modulus values were obtained using a constant-rate-of-crosshead movement testing machine in , ) 30 compression mode. The contact lens specimen to be tested is first sliced through in two cuts at right angles to each other, each cut going through the center of the lens (looking at the face of the lens), to form four pie-shaped pieces. This is done in order to insure that the specimen 35 will lie flat during the testing. The test piece is VTN-26 , 'J n 23 6 398 - 31 - compressed between two flat disks at a rate of 0.002 inch/minute. Compression stress and strain were monitored using a strip chart recorder at a chart speed of 2 inches/minute. The full scale deflection of the load cell is 0.110 pound. Zero compression was assumed when a load value of 0.005 pound was reached. The units of the compression modulus in the table are pounds per square inch. 10 —s 15 20 25 30 The oxygen permeability was measured by the method of Fatt et al., "Measurement of Oxygen Transmissibility and Permeability of Hydrogel Lenses and Materials", International Contact Lens Clinic, Vol. 9/No.2, March/April 1982, pages 76-88. The oxygen permeability is expressed as "Dk", where D represents the diffusion coefficient for oxygen in the material being tested, and k represents the solubiliby of oxygen in the material. The 2 units are (cm /sec)(ml 0,/ml x mmHg). (The numerical . -11 values given m the table should be multiplied by 10 to give the actual values.) Table V Hydrophobic Group Appearance % water Stiffness Dk None (control) (1) clear 60.4 20.2 30 benzyl clear 58.3 32.1 23 2-butyl clear 64.9 26.8 26 n-butyl clear 65.0 41.2 42 t-butyl clear 63.0 27.0 31 n-hexyl clear 61.3 43.2 30 2-ethylhexyl clear 59.0 38.1 30 n-octyl clear 64 .4 25.7 (2) 40 n-dodecyl clear 66.5 43.6 39 35 VTN-26 . t ■: 236 398 - 32 - (1) The formulation for the control was the following: HEMA 488.2 parts Methacrylic acid 8.2 parts 5 Ethylene glycol dimethacrylate 3.1 parts Trimethylolpropane trimethacrylate 0.49 part DAROCURE 1173 1.74 parts 48 parts of this monomer mixture were mixed with 52 parts of the previously described diluent. 10 (2) The low stiffness value found for this hydrogel is believed to be anomolous. To illustrate that oxygen transmissibility is greater for 15 thinner hydrogel contact lenses, the oxygen transmissibility Dk/1 was measured for contact lenses made of the same material but having different thicknesses. The lens material was made as described above, using as the hydrophobic groups 2-ethylhexyl and n-dodecyl. The 20 thicknesses and oxygen transmissibilities were as follows: Hydrophobic Group Thickness at Center Dk/1 25 2-ethylhexyl 110 18.9 X 10~9 it 60 29.3 X 10~9 II 30 37.8 X 10~9 n-dodecyl 110 20.2 X 10~9 30 II 60 29.9 X 10"9 II 30 43.0 X 10~9 35 VTN-26 . 4 I 236 398 - 33 - Control , J Preparation of hydrophobically modified HEMA by bulk polymerization with no diluent. To the following: 0.8g HEMA (including 0.0016g EGDMA and 0.032g MAA) 0.0028g DAROCURE 10 was added 0.2g of a hydrophobic ester of methacrylic acid. The mixture was prepared in a 20 ml pyrex scintillation vial. The mixture was deoxygenated with blowing nitrogen for 1 minute and sealed with a polyseal cap. The vials were laid on their side under two Philips TL20W/09N bulbs 15 such that the liquid level was between 5 and 6 cm from the lights. The material was photopolymerized for 10 minutes. The results are summarized in Table VI: -3\ 20 25 30 HYDROPHOBIC GROUP TABLE VI APPEARANCE before DOlvmerization after n-butyl clear clear 2-butyl clear clear t-butyl clear clear cyclohexyl clear clear n-hexy1 clear translucent benzyl clear clear n-octyl clear opaque n-dodecyl clear opaque n-stearyl clear opaque 2-ethylhexyl clear si. cloudy 35 It is believed that the translucency, opacity, or slight cloudiness that was observed in those lenses made by bulk VTN-2 6 23 6 3 98 - 34 - polymerization wherein the alkyl group in the alkyl methacrylate had 6 or more carbon atoms was caused by incompatibility that developed during the polymerization. </div>

Claims

<div class="application article clearfix printTableText" id="claims"> ? 3 6 3 9 8 - 35 - WHAT WE CLAIM IS:

1. Process for producing shaped hydrogel articles which comprises the steps of: (1) molding or casting a polymerization mixture comprising: (a) a monomer mixture comprising a major proportion of a hydrophilic (meth)acrylate ester monomer/ an alkyl (meth)acrylate wherein the alkyl group contains at least four carbon atoms/ and a cross-linking monomer; and (b) a water-displaceable diluent, wherein said diluent has a viscosity of at least 100 mPa.s at 30°C, and wherein said diluent consists essentially of a boric acid ester of certain dihydric alcohols, said dihydric alcohols having Hansen polar (wp) and Hansen hydrogen bonding (w^) cohesion parameters falling within the area of a circle defined as having a center at w^ = 20.5, wp = 13, and a radius of 8.5, to produce a shaped gel of a copolymer of said monomers and said diluent, and (2) thereafter replacing said diluent with water.

2. The process of Claim 1 wherein the said hydrophilic monomer is a hydroxyalkyl (meth)acrylate.

3. The process of Claim 2 wherein the hydroxyalkyl (meth)acrylate is 2-hydroxyethyl methacrylate.

4. The process of Claim 1 wherein said alkyl (meth)acrylate is n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, or n-dodecyl methacrylate. " - >s ,iw*;-1;236398;- 36 -;

5. The process of Claim 1 wherein said dihydric alcohol is 1,4-butanediol.;

6. The process of Claim 1 wherein said dihydric alcohol ^ 5 is diethylene glycol.;

7. The process of Claim 1 wherein the monomer mixture contains methacrylic acid.;10

8. The process of Claim 1 wherein the shaped hydrogel article is a contact lens.;

9. Process for producing contact lenses which comprises the steps of:;15 (1) molding or casting a polymerization mixture comprising:;(a) a monomer mixture comprising a major proportion of a hydrophilic (meth)acrylate ester, a cross-linking monomer, and an alkyl;20 (meth)acrylate wherein the alkyl group contains at least four carbon atoms; and;(b) a water-displaceable diluent, wherein said diluent has a viscosity of at least 100 mPa.s at 30°C, and wherein said diluent consists;25 essentially of a boric acid ester of certain dihydric alcohols, said dihydric alcohols having Hansen polar (wp) and Hansen hydrogen bonding (w^) cohesion parameters falling within the area of a circle defined as having a i^) 30 center at w^ = 20.5, wp = 13, and a radius of 8.5,;to produce a shaped gel of a copolymer of said monomers and said diluent, and (2) thereafter replacing said diluent with water.;35;VTN-2 6;1 :;- 37 -;

10. The process of Claim 9 wherein the said hydrophilic monomer is a hydroxyalkyl (meth)acrylate.;

11. The process of Claim 10 wherein the hydroxyalkyl 5 (meth)acrylate is 2-hydroxyethyl methacrylate.;

12. The process of Claim 9 wherein said diluent has a viscosity of at least 500 mPa.s at 30°C.;

13. The process of Claim 9 wherein said alkyl (meth)acrylate is n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, or n-dodecyl methacrylate.;15

14. The process of Claim 9 wherein said dihydric alcohol is 1,4-butanediol.;15. The process of Claim 9 wherein said dihydric alcohol is diethylene glycol.;20;16. The process of Claim 9 wherein the monomer mixture contains methacrylic acid.;17. A process for producing shaped hydrogel articles as 25 claimed in claim 1 substantially as herein described with reterence to the examples.;10;'-■-N;./;18. The process of claim 17 wherein the shaped hydrogel article is a contact lens.;30;19. A shaped hydrogel article whenever made by the process of any one of claims 1 to 8 and 17.;20. A contact lens whenever made by the process of any 35 one of claims 9 to 16 and 18.;WEST-WALKER, McCABE;*• WTORNGYS FOR THE APPLICANT ^ • o </div>